U.S. Pat. Nos. 5,201,186 and 5,222,368, which are assigned to the same assignee as the present application, disclose methods for detecting conditions which may cause shut down of a refrigeration unit, such as a transport refrigeration unit. When such a condition is detected, steps are taken to modify the operation of the refrigeration unit in an attempt to find an operating condition which will prevent, or at least delay, mandatory shut down. When mandatory shut down is still found to be required, an alarm code is stored which identifies the cause of shut down, and an alarm is generated which notifies a person in charge of the refrigeration unit, such as the driver of a truck or tractor-trailer unit which the refrigeration unit is associated with.
Certain types of refrigeration units, however, are required to reliably operate for relatively long periods of time without an attendant, such as transport refrigeration units which are associated with containers carried by rail. Thus, it would be desirable, and it is an object of the present invention, to provide additional protection against permanent shut down of a refrigeration unit.